Effects of photoperiod and temperature on pupal diapause induction of grape berry moth Lobesia botrana

Abstract. The grape berry moth, Lobesia botrana Denn. & Sciff. (Lepidoptera: Tortricidae), one of the most injurious pest of grape berries in Greece, is a multivoltine species that overwinters as diapausing pupae. The effects of several diel and non-diel photoperiods and of temperature, experienced by eggs and larvae, on pupal diapause induction were investigated. The diapause response curve was of Type I (long day type) and the determining factor was the duration of scotophase (> 11 h), regardless of the duration of photophase. However, at very short (< 4 h) photoperiods, the incidence of diapause was also high. Diapause was positively and significantly correlated with the egg-larval developmental time, pupal mortality and the duration of the pupal stage. Eggs and larvae reared under LD 12 : 12 h photoperiod and various temperatures (from 12 to 30 °C) produced diapausing pupae (almost 100%), but the duration of the pupal stage (intensity of diapause) increased with increasing temperature. Under continuous darkness, however, the percentage diapause decreased with increasing temperature. Single and double 1-h light pulses were applied systematically at various times during the scotophase of six diapause-inducing diel photoperiods. Two photosensitive points in time (called A and B) were revealed, during which illumination resulted in a significant decrease of diapause induction. The decrease was much greater during the first sensitive period (early in scotophase) rather than in the second (late in the scotophase).     

Diapause dynamics, seasonal phenology, and pupal color dimorphism of Papilio polyxenes in southern Florida, USA

In the European grapevine moth, Lobesia botrana (Denis and Schiffermüller) (Lepidoptera: Tortricidae), it has recently been shown that volatiles emitted from the main host plant, grapevine, are attractive to adult females. Here, using wind tunnel experiments, we tested the attractiveness of various grapevine, Vitis vinifera L. (Vitaceae), plant parts at different phenological stages, including ripe berries infested with the pathogenic fungus Botrytis cinerea (Persoon: Fries) (Sclerotiniaceae) to laboratory‐reared virgin and mated male and female moths. We also tested the attractiveness of the non‐host plant, tansy [Tanacetum vulgare (L.) (Asteraceae)], as flowers and flower volatiles were previously shown to be attractive to L. botrana females in the field. Mated female moths were the only adults to exhibit upwind orientation to grape plant parts in the flight tunnel. The most attractive parts of the grapevine plants were leaves, flower buds, and ripe berries. No attraction was observed to flowers. This corresponds to the phenological stages available when females of the 2–3 generations during a year are present in the field. No attraction was observed to leaves and flowers of tansy.     

滞育昆虫营养物质的积累、转化与调控

滞育是昆虫度过不良环境的一种生存适应策略,营养物质的利用、积累和转化影响昆虫的滞育。滞育期间,昆虫体内发生一系列生理生化变化,包括脂类、碳水化合物和氨基酸等内源营养物质呈特异性地积累或转化,保障了滞育个体在逆境中存活及滞育解除后发育的能量需求。外源营养物质对昆虫滞育的影响较复杂,其种类、丰度、质量能通过"食料-寄主-天敌"营养关系进行传递,影响昆虫体内营养物质的积累和转化,改变昆虫的耐寒性、滞育率等,制约昆虫的滞育深度、滞育存活率。滞育昆虫营养物质积累、利用机制复杂多样,胰岛素信号通路-叉头转录因子以及激脂激素的调控效应在滞育诱导及营养物质转化中起到了关键的调控作用,但滞育的系统性调控仍需进一步深入研究。     

Olfactory and gustatory behaviour by larvae of shape Lobesia botrana in response to shape Botrytis cinerea

In vineyards, larvae of Lobesia botrana (Denis and Schiffermüller) (Lepidoptera: Tortricidae) and Botrytis cinerea (Persoon: Fries) often occur together. This study was carried out to establish whether first instar larvae are attracted by the fungus. Olfactory and gustatory responses of larvae to the fungus were investigated on grape berry clusters (Vitis vinifera) and in two types of olfactometer. In clusters infected partly by B. cinerea, 82% of first instar larvae settled where berries had been infected. In the olfactometers, first instar larvae detected and discriminated between two tested foods. They significantly preferred synthetic media or grape berries (cv., 'Alphonse Lavallée' or 'Cabernet Sauvignon') infected with B. cinerea to non-infected controls. The olfactory response led to 62.2% to 72.6% of the first instar larvae attracted by the fungus and the association of olfactory with gustatory responses resulted in similar rates (64.1% to 81.6%). So, the larvae were most attracted by synthetic media or grape berries infected by the fungus as compared to the controls. Olfaction appears to be the main sense involved in this attraction process.     

Geographic and parental influences on diapause by a polyphagous insect herbivore

1 Facultative diapause permits insects to initiate an additional generation when conditions are favourable, or to enter diapause when they are not. Although the principle environmental cues for diapause induction are often temperature and photoperiod, we demonstrated recently that the quality of host plant consumed by the larvae of Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) influences the proportion of larvae that enter diapause and therefore voltinism. 2 Previous work has also suggested that non‐Mendelian parental effects influence diapause by C. rosaceana larvae, but the mechanism was not established. Here, we report further evidence for parental effects on diapause and examine whether parental diet influences diapause induction. 3 We collected larvae of C. rosaceana from six sites at three latitudes in the Province of Québec. There was an increase in the proportion of larvae entering diapause with increasing latitude. Rearing larvae under identical conditions on artificial diet for two generations significantly reduced variation in diapause among populations within a given latitude, and supported the existence of parental effects that influence offspring diapause. 4 Experiments with different host plants and high‐ vs. low‐quality artificial diets provided no evidence that the parental effects on offspring diapause were based on the quality of food consumed by parents. Diapause in C. rosaceana appears influenced by a hierarchy of cues, including temperature, photoperiod, current larval diet and parental environment.     

Vitamin C content in plants is modified by insects and influences susceptibility to herbivory

Analysis of a diverse cross‐sample of plant‐insect interactions suggests that the abundance of vitamin C (L ‐ascorbic acid, ascorbate or AsA) in plants influences their susceptibility to insect feeding. These effects may be mediated by AsAs roles as an essential dietary nutrient, as an antioxidant in the insect midgut, or as a substrate for plant‐derived ascorbate oxidase, which can lead to generation of toxic reactive oxygen species. Ascorbate can also influence the efficacy of plant defenses such as myrosinases and tannins, and alter insects' susceptibility to natural enemies. Conversely, herbivores appear to influence both de novo synthesis and redox cycling of AsA in their host plants, thereby potentially altering the nutritional value of crops and their susceptibility to pests. The recent development of genetically modified crops with enhanced AsA content provides both an impetus and a tool set for further studies on the role of AsA in plant‐insect interactions.     

Chemical contents of Macaranga food bodies: adaptations to their role in ant attraction and nutrition

1. Macaranga (Euphorbiaceae) is a paleotropical tree genus comprising myrmecophytic and non-myrmecophytic species. All species are presumed to possess food bodies (FBs) to maintain or attract ants as anti-herbivore defence.
2. The hypothesis was tested that Macaranga species differing in their mode of association with ants would produce FBs differing in their chemical composition. We investigated contents of carbohydrates, proteins and lipids in FBs of four myrmecophytic and one non-myrmecophytic Macaranga as well as one Parthenocissus (Vitaceae) species.
3. On a dry weight basis, FBs of myrmecophytes contained relatively higher amounts of proteins compared to carbohydrates than those of non-myrmecophytes. Soluble carbohydrates showed species-specific patterns and were found in especially high amounts in both non-myrmecophytes. Furthermore, Parthenocissus FBs contained higher amounts of soluble compared to polymerous substances not only in carbohydrates but also in proteins.
4. FBs seem to be specifically adapted to their respective role in ant attraction and nutrition, with myrmecophytes providing ants with high amounts of lipids and proteins and non-myrmecophytes mainly offering carbohydrates in the form of common soluble sugars.     

Growth and fecundity of Daphnia after diapause and their impact on the development of a population

Laboratory and field investigations revealed that the life history traits of exephippial and parthenogenetic generations of Daphnia differ substantially. Daphniids hatching from resting eggs grow faster and their definitive body sizes are bigger than of hatchlings from subitaneous eggs. Size at maturity for exephippial animals is significantly larger. In spite of this, they mature a few days earlier than parthenogenetic females. In this study, the difference was 3–4 days for the laboratory experiments and 1–3 days for the field. Fecundity of the exephippial generation is markedly higher. Here, the clutch size for this generation was up to 3.5–4.0 times as large as for the parthenogenetic generation. Moreover, obtained results suggest that the relationship between clutch size and body length for both generations differ significantly.Estimates of the intrinsic rate of increase for field Daphnia populations demonstrated that life history traits of exephippial animals lead to a two or threefold higher rate of increase in the conditions of invertebrate predation pressure. Under moderate fish pressure, obtained r values for the daphniids hatching from resting eggs were larger than those from subitaneous. High growth rate of exephippial females is disadvantageous only under the conditions of severe pressure by fish. Obtained results suggest that hatchlings from diapausing eggs an acceleration of population increase by several times during the beginning of the development of a population with periodical re-establishment from resting eggs.     

Effects of added nitrogen on leaf nitrogen concentration and population dynamics of insects associated with Rumex obtusifolius L.

A series of experiments was designed to study the effects of changes in leaf nitrogen (N) concentration on population dynamics of a range of insects associated with Rumex obtusifolius. During the study period, the N concentration in leaves fluctuated between 2 and 6% dry weight. The insects at both study sites showed a pattern of shift in time for peak population density (time‐shift). This suggests that the insect community dynamics might be closely related to the allocation and distribution of resources by the host‐plant. The elevated N concentration in the host‐plant did not change the temporal order of the peak population densities of the insects, although it may determine the time for the optimal exploitation of resources by each insect species.     

Very long diapause and extreme resistance to population disturbance in a galling insect

1. Some insects have a prolonged diapause – a dormancy that extends over more than 1 year. In most species prolonged diapause involves one or a few extra years, but in extreme cases diapause may surpass 10 years. Few cases of very long diapause have been described, and very little is known about the population consequences of the temporal refuge formed by the diapausing individuals. 2. The gall midge Contarinia vincetoxici Kieffer galls the flowers of a long‐lived herb Vincetoxicum hirundinaria Med. After completing development, larvae leave the galls for the ground where they enter diapause. Extending an earlier published inoculation experiment, we show that the diapause may last up to at least 13 years, with a median duration of at least 6 years. 3. The gall midge is attacked by two parasitoid species. Dissections of gall midge larvae for presence of parasitoids revealed that Omphale salicis Haliday had a maximum 2 year diapause and Synopeas acuminatus Kieffer a maximum 4 years. The very long diapause of the gall midge may thus provide a temporal refuge from these enemies. 4. In a 15‐year field experiment all galls were removed every year from six isolated habitat patches. Density changes in experimental populations were not statistically different from control populations for over a decade. After 14–15 years a modest decline could be observed. This slow response illustrates that prolonged diapause in C. vincetoxici provides a very strong population buffer against mortality during the galling stage.     

Feeding behaviour, sensory physiology and nutrient feedback: a unifying model

The design features of gustatory systems are considered in relation to the need for insect herbivores (or indeed any animal) to regulate their nutrient intake. The gustatory system (defined to include both peripheral and central components) should ideally be designed to reflect: (a) the average nutritional requirements of the insect during its various developmental stages; (b) the predictably unpredictable variation in nutrient supply-demand which occurs about that average; and (c) the distribution and composition of foods available in the environment. A mathematical model is presented which makes detailed predictions regarding behavioural and electrophysiological responses to foods or simple solutions varying in nutrient content.     

Seasonal variation in generation time, diapause and cold hardiness in a central Ohio population of the flesh fly, Sarcophaga bullata

Abstract.

• 1 Generation time, diapause phenology and cold tolerance of the flesh fly, Sarcophaga bullata, were examined under confined natural conditions in central Ohio. In this locality, the fly can complete a maximum of four generations annually.
• 2 Very few pupae entered diapause in the first and second generations (May to July in 1988). In the third generation (August) 37% of the pupae entered an overwintering diapause, as did all pupae from the fourth generation (September).
• 3 The adult eclosion date in the spring and annual generation time can be predicted accurately from degree day data.
• 4 Cold tolerance of the field-overwintering portion of the population was high. After 30 days under field conditions, diapausing pupae readily survived a 7-day exposure to — 17°C. Glycerol appears to be the major cryoprotectant in S.bullata, and glycerol concentrations in the field population (95–142 mm ) remained high throughout the winter.
• 5 In contrast, diapausing flies reared under laboratory conditions (20°C, 12:12 LD) were less cold tolerant, and glycerol concentrations were lower (6.9–21.2 mm ). Field conditions thus promote the acquisition of high levels of cold tolerance, presumably as a consequence of the accumulation of higher concentrations of glycerol.
• 6 In spite of differences in the cold tolerance of laboratory and field flies, the supercooling points of the two groups of flies were nearly the same, thus implying that the supercooling point is not a good indicator of cold tolerance.

     

Stored-product insects in a flour mill: population dynamics and response to fumigation treatments

In a wheat flour mill, seasonal trends in stored‐product insect trap capture, relationships between trap captures inside and outside the mill, and between pheromone trap capture and product infestation, and the impact of fumigation on pest populations, were assessed. Mark‐recapture was used to evaluate the potential for movement of insects outside the mill into the mill. For Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) and Trogoderma variabile Ballion (Coleoptera: Dermestidae), pheromone trap captures outside were higher than inside the mill, and when inside and outside trap captures were correlated, both indoor and outdoor trap captures tended to cycle according to a seasonal pattern; fumigations did not consistently influence pheromone trap captures, and in only one instance were they found in product samples. Mark‐recapture data indicated that P. interpunctella was capable of entering the building from outside. Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) trap captures, in contrast, tended to be lower outside compared to inside, followed a pattern of sharp decline after fumigation treatment, and then steadily increased (0.002–0.005 beetles/trap/day) until the next fumigation. This pattern, other than potentially the rate of increase, was not impacted by season and outside trap capture levels. Tribolium castaneum was the primary species infesting the product. The information generated in this study provides some of the information needed to develop improved monitoring and management programs.     

Rainfall and host reproduction regulate population dynamics of a specialist seed predator

1. Mast seeding is a widespread resource pulse caused by synchronized and intermittent production of a large seed crop by plant populations. The effects of masting on wildlife have been well documented in granivorous vertebrates, but less is known about its impact on population dynamics of insects. 2. This study investigated, over 6 years, variation in abundance of a specialist weevil (Curculio elephas) preying on holm oak (Quercus ilex) acorns. 3. An immediate bottom-up effect of seed production on weevil larval abundance was detected, which was driven by an increase in realised fecundity and aggregation at seed-rich trees. Moreover, trees producing on average more and larger acorns sustained larger weevil populations. However, no correlation was found between current and previous year adult abundance, suggesting that C. elephas did not capitalise on the reproductive bottom-up effect. 4. It was rainfall, not masting, that most strongly shaped the temporal variation in insect abundance. Rainfall facilitates emergence after diapause at underground earth cells and was also responsible for among-tree synchronisation in adult weevil population dynamics. 5. In spite of their trophic specialisation, not only food availability, but also weather affects weevil numbers. The present results indicate that moving beyond bottom-up effects is required to better understand complex systems that involve masting plants and insects that consume their seeds.     

The importance of hatching from resting eggs for population dynamics and genetic composition of Daphnia in a deep reservoir

1. Cyclical parthenogens, organisms switching between sexual and asexual mode of reproduction, are common in aquatic habitats. In permanent waterbodies with year‐round persistence of populations, the relevance of sexually produced resting eggs for population dynamics and structure is still largely unexplored. 2. The aim of this study was to investigate the importance of recruitment from resting eggs to Daphnia spp. in a deep dimictic reservoir with overwintering populations (Saidenbach Reservoir, Germany). We linked field studies on Daphnia population dynamics, hatching rates and diapausing egg abundances in the sediment with allozyme analysis of the genetic variability of both the pelagic population and hatchlings from resting eggs. 3. We found higher hatching rates at intermediate depths (10–18 m), although highest diapausing egg abundances were found in the deeper parts of the reservoir. From the extensive field data, we calculated a population budget for the main basin of the reservoir, which showed that hatched daphnids accounted for <1% of the total abundance and explained only a tiny fraction of population growth. 4. The genetic composition (MultiLocus Genotypes, MLG) of the pelagic population was relatively stable throughout the stratified period with up to five among 39 detected MLGs attaining frequencies >5% per date. From 11 MLGs differentiated among hatched daphnids, three were recovered in the pelagic population in perceptible, albeit low frequencies (1–4%). 5. We conclude that the contribution of hatched animals to the spring population dynamics is negligible in situations with an overwintering population present and will only become relevant if densities are extremely low. In this type of system, the significance of the resting egg bank is presumably mainly related to the maintenance of genetic diversity.     

Efficacy of a Cladosporium sp. fungus against Helicoverpa armigera (Lepidoptera: Noctuidae), other insect pests and beneficial insects of cotton

A strain of the fungus Cladosporium sp. (RM16) from an egg of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) was assessed as a potential biocontrol agent for this pest. Pathogenicity of the fungus was tested against H. armigera eggs and larvae, cotton aphids (Aphis gossypii Glover; Homoptera: Aphididae), and silverleaf whitefly type B (Bemisia tabaci Gennadius; Hemiptera: Aleyrodidae). The pathogenicity of the fungus to the predatory red and blue beetles (Dicranolaius bellulus Guérin-Méneville; Coleoptera: Melyridae), transverse ladybird beetles (Coccinella transversalis Fabricius; Coleoptera: Coccinellidae), green lacewings (Mallada signatus Schneider; Neuroptera: Chrysopidae) and damsel bugs (Nabis kinbergii Reuter; Hemiptera: Nabidae), was also assessed in the laboratory. Fungus treatment resulted in failure to hatch of up to 64% of H. armigera eggs (compared with 11% in the controls) and mortality of 54% of first instar H. armigera larvae (compared with 5% in the controls). In contrast, it was not pathogenic to later instar H. armigera larvae. Cladosporium RM16 was also efficacious against the sap-sucking insect pests of cotton that were tested. No significant harmful effect of the fungus was found on any of the four beneficial predatory insects assessed in this study. Cladosporium RM16 has the potential as biological control agent to support integrated pest management in cotton farming systems, although this needs intensive study.     

Feeding ecology of three predacious aquatic insects and two fish in a riffle of the Speed River,Ontario

The food habits of two fish (Etheostoma flabellare and Rhinichthys atratulus) and three predacious aquatic insects (Nigronia serricornis, Paragnetina media and Agnetina capitata) were examined for one year in a riffle of the Speed River, Ontario. Adult E. flabellare fed primarily on net-spinning caddisflies whereas juvenile E. flabellare relied heavily on chironomids. Rhinichthys atratulus had a more varied diet composed of chironomids, Antocha larvae (Tipulidae) and net-spinning caddisflies. Two of the aquatic insect predators consumed large numbers of net-spinning caddisflies; however, P. media contained large percentages of Hydropsyche and Cheumatopsyche whereas N. serricornis fed primarily on non-hydropsychid net-spinners. The diet of A. capitata was composed largely of chironomids and mayflies. Schoener's diet overlap index () suggested that large E. flabellare and P. media had similar diets; however, E. flabellare ingested much larger prey than P. media. Adult E. flabellare contained a significantly greater proportion of larger prey items in comparison with benthic samples whereas similar comparisons with other predators showed no selection for larger prey. These data demonstrate that E. flabellare was size selective given the range of prey sizes available whereas the other predators were not. Also, there was little dietary overlap among the fish and invertebrate predators suggesting a partitioning of resources.     

Plant defensin MtDef4-derived antifungal peptide with multiple modes of action and potential as a bio-inspired fungicide

Chemical fungicides have been instrumental in protecting crops from fungal diseases. However, increasing fungal resistance to many of the single-site chemical fungicides calls for the development of new antifungal agents with novel modes of action (MoA). The sequence-divergent cysteine-rich antifungal defensins with multisite MoA are promising starting templates for design of novel peptide-based fungicides. Here, we experimentally tested such a set of 17-amino-acid peptides containing the γ-core motif of the antifungal plant defensin MtDef4. These designed peptides exhibited antifungal properties different from those of MtDef4. Focused analysis of a lead peptide, GMA4CG_V6, showed that it was a random coil in solution with little or no secondary structure elements. Additionally, it exhibited potent cation-tolerant antifungal activity against the plant fungal pathogen Botrytis cinerea, the causal agent of grey mould disease in fruits and vegetables. Its multisite MoA involved localization predominantly to the plasma membrane, permeabilization of the plasma membrane, rapid internalization into the vacuole and cytoplasm, and affinity for the bioactive phosphoinositides phosphatidylinositol 3-phosphate (PI3P), PI4P, and PI5P. The sequence motif RRRW was identified as a major determinant of the antifungal activity of this peptide. While topical spray application of GMA4CG_V6 on Nicotiana benthamiana and tomato plants provided preventive and curative suppression of grey mould disease symptoms, the peptide was not internalized into plant cells. Our findings open the possibility that truncated and modified defensin-derived peptides containing the γ-core sequence could serve as promising candidates for further development of bio-inspired fungicides.     

Survivability and post‐diapause fitness in a scolytid beetle as a function of overwintering developmental stage and the implications for population dynamics

1. It has recently been suggested that expected increases in temperature might lead to an additional generation per season in bark beetles. Thus, populations would grow more rapidly. However, an additional but not fully developed generation could lead to high winter mortality in the pre‐imaginal stages. 2. Winter survivability and post‐diapause fitness as a function of the overwintering developmental stage of the spruce bark beetle Ips typographus L. were studied along an altitudinal cline. Fitness was tested in terms of weight, lipid content and flight capacity. 3. Mortality was significantly lower and emergence per brood system significantly higher for fully developed adults that entered overwintering than for larvae, pupae or callow adults. 4. Post‐diapause fitness in terms of dry weight and flight capacity was significantly higher in individuals that completed development before winter, and lipid contents also showed a trend for being higher in those individuals. 5. In conclusion, in a scenario where effective temperature sums are not adequate for the complete development of an additional generation, models may overestimate population growth by neglecting increased mortality and reduced post‐diapause fitness. The results highlight the importance of considering life‐history traits and indirect effects in addition to abiotic factors such as temperature when modelling population dynamics.